1. Field of the Invention
The invention concerns a support body comprising several support elements which are lined up one behind the other in the direction of the axis of the low-temperature cable being supported. More particularly, the invention concerns a support body whose elements comprise support rings which enclose the cable axis, are arranged one behind the other at predetermined spacings and receive layers of individual conductors, particularly superconductors in wire or ribbon form, which are concentric with respect to the cable axis.
2. Description of the Prior Art
D-c and also three-phase cables, whose conductors are cooled to low temperatures and are, for instance, superconducting, can advantageously be made flexible, so that they can be wound on cable drums and can easily be installed in the field. The conductors of these cables typically comprise one or more layers of individual conductor wires or ribbons such as, for instance, individual aluminum wires which are coated on their outer surface with a superconducting layer. These layers of conductor wires or ribbons are, in general, arranged on the outer circumference of support bodies and, in addition, are often twisted so that the length of the cable is independent of temperature and, thus, remains constant when the cable is cooled down to a low temperature (U.S. Pat No. 3,541,221).
In the U.S. Pat. No. 3,668,297, a flexible low-temperature cable is disclosed whose tubular conductor comprises individual helical conductors. The individual conductors are each of an approximately rectangular cross section and are arranged at a mutual spacing on the outer circumference of a plastic support body. The latter support body comprises either support rings which may, additionally, be held against each other by means of wires, or a support helix which may include a wide helix of plastic upon which an additional narrow helix is placed.
A further support arrangement is known from the U.S. Pat. No. 3,691,287. This support arrangement contains several support rings which, together with an armor of foil or ribbon, are combined to form a hose-like structure capable of supporting a load. The support rings may, additionally, be loosely connected with each other by rods.
To fabricate a low-temperature cable with ring or helix type support elements, rigid guides are necessary, if the individual ribbon or wire conductors are to be applied to the outer surfaces of these support elements. As the required guidance must be carried out in the available cabling machines over long distances of, for instance, 20 m, difficulties are encountered in winding the support bodies formed from such support elements. These difficulties involve the use in the cabling machines of additional means for preventing the elongation or compression of the helical support elements or the axial displacement of the ring support elements.
There is also a danger that in a cable formed with support bodies comprised of helical or ring-type support elements the elements may become displaced as a result of temperature gradients which occur in the cooling-down and heating-up processes. The resultant diameter changes occurring in the case of the helical support elements, as well as the spacing changes occurring in the case of the support ring elements, cause the individual conductors supported by these elements to be less well secured. As a result there is a danger of conductor motion and thereby, a danger that individual conductor sections will become normal-conducting.
It is therefore an object of the present invention to improve the design of support elements of the type disclosed in the U.S. Pat. No. 3,691,287. In particular, a support element is to be provided which exhibits satisfactory mechanical stability, while still being sufficiently flexible and transparent for a coolant.